Photobleaching method

ABSTRACT

The present disclosure provides an improved method for photobleaching an eye of a subject. The disclosed method may be used in a number of psychophysical test methods, including, but not limited to, measurement of dark adaptation. The improved method for photobleaching involves at least one of the following improvements: (i) the use of a bleaching light emitting a particular wavelength of light or a tailored spectrum of wavelengths; (ii) restricting or otherwise spatially tailoring the region of the retina that is subject to photobleaching; and (iii) utilizing a bleaching light having an intensity that is at or below the intensity of ambient daylight. The present disclosure additionally provides a combination of a photobleaching light and an apparatus to administer a psychophysical test suitable for use in practicing the disclosed methods.

FIELD OF THE DISCLOSURE

The present disclosure relates to improved methods for photobleaching aneye, or a desired portion thereof, of a subject.

BACKGROUND

The retina is comprised of a thin layer of neural cells that lines theback of the eyeball of vertebrates. In vertebrate embryonic development,the retina and the optic nerve originate as outgrowths of the developingbrain. Hence, the retina is part of the central nervous system. Thevertebrate retina contains photoreceptor cells (both rods and cones)that respond to light; the resulting neural signals then undergo complexprocessing by neurons of the retina. The retinal output takes the formof action potentials in retinal ganglion cells whose axons form theoptic nerve.

One component of the retina is the macula. The macula of the human eye,which is about 6 mm in diameter and covers the central 21.5 degrees ofvisual angle, is designed for detailed vision. The macula itselfcomprises a small cone-dominated fovea surrounded by a rod-dominatedparafovea (Curcio 1990, J. Comp. Neurol. 292:497). Rods are responsiblefor vision in dim light (scotopic vision) while cones are responsive tobright light and colors (photopic vision). In young adults, the numberof rods outnumbers cones by approximately 9:1. This proportion of rodsto cones changes as individual's age.

The function of the rod and cone photoreceptors is impacted by thehealth of the rod and cone photoreceptors themselves. The health andfunction of the rod and cone photoreceptors are maintained by theretinal pigment epithelium (RPE), the Bruch's membrane and thechoriocapillaris (collectively referred to as the RPE/Bruch's membranecomplex). The RPE is a dedicated layer of nurse cells behind the neuralretina. The RPE sustains photoreceptor health in a number of ways,including, but not limited to, maintaining proper ionic balance,transporting and filtering nutrients, providing retinoid intermediatesto replenish photopigment bleached by light exposure and absorbing strayphotons. The RPE and the photoreceptors are separated by thechoriocapillaris, which provides blood flow to the neural retina.Further separating the RPE and the choriocapillaris is the Bruch'smembrane, a delicate vessel wall only 2-6 μm thick.

The impairment of the rod and/or cone photoreceptors may lead toimpairment in dark adaptation and other visual processes. Darkadaptation is defined as the recovery of light sensitivity by the retinain the dark after exposure to a conditioning light. In this regard, darkadaptation and other visual processes can essentially be viewed as abioassay of the health of the rod photoreceptors, the RPE, the Bruch'smembrane and the choriocapillaris, and impaired dark adaptation and theimpairment of other visual functions may be used as a clinical marker ofdisease states that impair one or more of the rod and/or conephotoreceptors, the RPE, the Bruch's membrane and the choriocapillaris.For impairments in dark adaptation such disease states include, but arenot limited to age-related macular degeneration (AMD; which is alsoknown as age-related maculopathy ARM), vitamin A deficiency, Sorsby'sFundus Dystrophy, late autosomal dominant retinal degeneration, retinalimpairment related to diabetes and diabetic retinopathy .

A subject's ability to dark adapt can be characterized by measuringscotopic sensitivity recovery (i.e., rod function) after photobleachingusing psychophysical testing methods known in the art. In suchpsychophysical tests, typically a test eye of the subject is firstpre-conditioned to a state of relative scotopic insensitivity byexposing the eye to a conditioning light (a procedure referred to asphotobleaching or bleaching). After this pre-conditioning (or bleaching)step, the subject's scotopic sensitivity (the minimum light intensitythat can be detected in a dark environment) is measured at one or moresuccessive times. The measurement is made by exposing the bleachedregion of the test eye to a series of stimulus lights of varyingintensities. Based on subject feedback as to which stimulus intensitiescan be detected, a sensitivity, or threshold, is determined for eachsuccessive time. The subject is kept in a dark environment throughoutthe test. The absolute levels and/or kinetics of the resulting thresholdcurve indicate the subject's ability to dark adapt. Impairment in thesubject's dark adaptation parameters may indicate the subject iscurrently suffering from and/or at risk for a disease state that impairsone or more of the rod and/or cone photoreceptors, the RPE, the Bruch'smembrane and the choriocapillaris.

The bleaching procedure is a critical element in the usefulness andutility of methods used to measure dark adaptation and in otherpsychophysical tests. Although it is well known that cones (thephotoreceptors in the retina primarily responsible for photopicsensitivity) and rods (the photoreceptors in the retina primarilyresponsible for scotopic sensitivity) have different spectral responsecurves, existing photobleaching protocols used in psychophysical testssuch as dark adaptation and dark adaptometers and other instruments usedin such psychophysical tests invariably rely on white (achromatic) orvery broadband light to achieve the desired photobleaching. Furthermore,all or a major portion of the retina area is photobleached, and thebleaching light intensity is set above ambient daylight (i.e., it has anintensity above the intensity of ambient daylight). The use ofachromatic light, bleaching of all or a majority of the retina duringthe photobleaching process and the use of higher intensity bleachinglights can increase the duration of the psychophysical test, such asdark adaptation, can increase patient burden and discomfort duringtesting and can lead to greater test-to-test variation and/ormeasurement bias caused by variable lens opacity or other factors, withcorresponding problems in interpretation of the psychophysical tests.The chromatic composition of the bleaching light, the portion of theretina area that is photobleached and the bleaching intensity can allhave profound affects on the duration of the test, patient burden,test-to-test variability and measurement bias.

Therefore, the art is lacking an improved method of photobleaching foruse with psychophysical tests, such as but not limited to, darkadaptation, and for use with instruments used in implementing suchpsychophysical tests. The present disclosure provides such an improvedmethod of photobleaching, along with bleaching lights for use in thedisclosed methods, and exemplary devices incorporating such bleachinglights and suitable for use in practicing the disclosed methods. Suchdisclosures were not heretofore appreciated in the art.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows various peak absorption profiles for the S, M and L conesand rod photoreceptors.

FIG. 2A shows a theoretical illustration of a dark adaptation curve fora normal individual obtained using a broad, achromatic photobleachinglight and a 505 nm stimulus target.

FIG. 2B shows a theoretical illustration of a dark adaptation curve fora normal individual obtained using a photobleaching light emitting arange of wavelengths centered on 505 nm and a target stimulus of 505.

FIG. 3A shows a theoretical illustration of a dark adaptation curve fora normal individual obtained using a broad, achromatic bleaching lightand a 505 nm target stimulus.

FIG. 3B shows a theoretical illustration of a dark adaptation curve fora normal individual obtained using a photobleaching light emitting arange of wavelengths centered on 560 nm and a stimulus target centeredon 450 nm.

FIG. 4A shows a dark adaptation curve generated using a photobleachinglight emitting an achromatic white light comprising a broad range ofwavelengths from about 400 to about 700 nm,

FIG. 4B shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of wavelengths centered on only theblue (about 405 nm to about 425 nm) spectrum.

FIG. 4C shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of wavelengths centered on only thegreen (about 490 nm to about 510 nm) spectrum.

FIG. 4D shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of wavelengths centered on only thenarrow red (about 640 nm to about 660 nm) spectrum.

FIG. 5 shows the results of a preference test conducted comparing aphotobleaching light emitting an achromatic white light comprising abroad wavelength spectrum of about 400 nm to about 700 nm and ableaching light emitting a tailored spectrum of light consistingessentially of wavelengths of about 490 nm to about 510 nm (greenspectrum).

FIG. 6A shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of light consisting essentially ofwavelengths of about 490 nm to about 510 nm (green spectrum).

FIG. 6B shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of light consisting essentially ofwavelengths of about 490 nm to about 510 nm (green spectrum) with theaddition of a blue absorption filter placed in from of the testsubject's eye.

FIG. 6C shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of light consisting essentially ofwavelengths of about 440 nm to about 460 nm (blue spectrum).

FIG. 6D shows a dark adaptation curve generated using a photobleachinglight emitting a tailored spectrum of light consisting essentially ofwavelengths of about 440 nm to about 460 nm (blue spectrum) with theaddition of a blue absorption filter placed in from of the testsubject's eye.

FIG. 7A shows a dark adaptation curve generated using a bright,achromatic white photobleaching light having an intensity above theintensity of ambient daylight.

FIG. 7B shows a dark adaptation curve generated using a dim (uniformbleaching field having an intensity below the intensity of ambientdaylight.

FIG. 8A shows a dark adaptation curve generated using a photobleachinglight emitting an achromatic white light comprising a broad wavelengthspectrum of about 400 to about 700 nm for both normal test subjects andtest subjects having age-related maculopathy (ARM).

FIG. 8B shows a dark adaptation curve generated a photobleaching lightemitting a tailored spectrum of light consisting essentially ofwavelengths of about 490 nm to about 510 nm (green spectrum) for bothnormal test subjects and test subjects having age-related maculopathy(ARM).

FIG. 9A shows an internal side view of one embodiment of an apparatuscombination for photobleaching a subject's eye.

FIG. 9B shows a front view of the apparatus combination of FIG. 9A.

DETAILED DESCRIPTION General Description

Rhodopsin and cone pigments are the visual pigments contained in theouter portions of the rod and cone photoreceptors of the retina,respectively. As the visual pigment absorbs light, it breaks down intointermediate molecular forms and initiates a signal that proceeds down atract of nerve tissue to the brain, allowing for the sensation of sight.The outer segments of the rods and cones contain large amounts of thesepigments, stacked in layers lying perpendicular to the light incomingthrough the pupil. There are five types of visual pigment in the retina,with slight differences that allow for differences in visual perception.Rhodopsin is the visual pigment in the rods and allows for scotopicvision. Rhodopsin in the rods absorbs light energy in a broad band ofthe electromagnetic spectrum peaking at 505 nm. There are three types ofvisual pigments in the cones, each with a slightly different peakabsorption: short wavelength (S) cones have a spectral response peakingaround 419 nm (the blue spectrum), medium wavelength (M) cones have aspectral response peaking around 531 nm (the green spectrum), and longwavelength (L) cones have a spectral response peaking around 558 nm (thered spectrum). The visual pigments in the cones allows for photopicvision. The various peak absorption profiles for the S, M and L conesand rod photoreceptors are shown in FIG. 1. Furthermore, about 1% ofhuman retinal ganglion cells are photoreceptors. These light sensitiveganglion cells contain melanopsin photopigment, which have a spectralresponse peaking around 460 nm, These cells are thought to help regulatecircadian photoentrainment. Depriving these ganglions cells of 460-nmlight is hypothesized to disturb sleep/wake cycles in humans.

The following is a description of the biochemistry of rhodopsin,although the biochemistry of the cone pigments and melanopsion isthought to be very similar. Rhodopsin consists of 11-cis-retinal and theprotein opsin, and is tightly hound in the outer segment of the rods,11-cis-retinal is the photoreactive portion of rhodopsin, which isconverted to all-trans-retinal when a photon of light in the activeabsorption band strikes the molecule. This process goes through asequence of chemical reactions as 11-cis-retinal isomerizes toall-trans-retinal. During this series of chemical steps, the nervefiber, which is attached to that particular rod or cone, undergoes astimulus that is ultimately perceived in the brain as a visual signal.Following the breakdown of 11-cis-retinal to all-trans-retinal, the11-cis-retinal is regenerated by a series of steps that result in11-cis-retinal being recombined with opsin protein. The isomerization toall-trans-retinal is the reaction that occurs during the bleachingprocess.

The present disclosure provides an improved method for photobleaching aneye of a subject. The improved photobleaching process is achieved byusing at least one of the following modifications to prior art bleachingprotocols: (i) the use of a bleaching light emitting a particularwavelength of light or a tailored spectrum of wavelengths; (ii)restricting or otherwise spatially tailoring the region of the retinathat is subject to photobleaching; and (iii) utilizing a bleaching lighthaving an intensity that is at or below the intensity of ambientdaylight. Such improvements to the prior art bleaching protocols for usein psychophysical tests, whether alone or in various combinations, havenot been previously appreciated in the art. Likewise, instruments usingthe improved photobleaching methods and light source disclosed hereinand improved instruments for administering psychophysical tests are alsoprovided.

Using the improved photobleaching methods described herein, certaindisadvantages associated with the prior art photobleaching methods arereduced or eliminated, resulting in a psychophysical test that is moreefficient to administer and is shorter in duration. Furthermore, thepatient burden and patient discomfort using the improved photobleachingmethod described herein is significantly reduced. Finally, the improvedbleaching method described herein increases the accuracy andreproducibility of psychophysical tests by reducing test-to-testvariation and measurement bias caused by pre-existing conditions.Therefore, such psychophysical tests are more accurate and easier tointerpret.

The improved bleaching method described herein can be used in anypsychophysical test or other testing procedure where photobleaching of asubject's eye is required. The present disclosure describes the use ofthe bleaching method disclosed in conjunction with measurements of darkadaptation as one example of application. However, the teachings of thepresent disclosure should not be limited to the use of the bleachingmethods described to measurements of dark adaptation or any other singlepsychophysical test. The teachings of the present disclosure may be usedin combination with any visual function test or any psychophysical testknown in the art that requires bleaching the eye of the subject, or aportion thereof.

Psychophysical tests measure a subject's sensation and perception ofphysical stimuli. The stimuli can be visual, auditory, olfactory,tactile or gustatory. Visual stimuli include, for example, varyingintensities of light, differing colors, and different sizes of text.Psychophysical tests using visual stimuli include, for example, darkadaptometry, visual sensitivity tests, spatial resolution acuity tests,contrast sensitivity tests, flicker photometry, photostress tests,Vernier acuity tests, colorimetry, motion detection tests, objectrecognition, and perimetry. Psychophysical tests can be used to assessthe status of visual functions including, for example, dark adaptation,photopic sensitivity, scotopic sensitivity, visual acuity, colorsensitivity, contrast sensitivity, color discrimination, and visualfield. Psychophysical tests can be used to diagnosis the risk, presenceor severity of eye diseases including, for example, age-related maculardegeneration, vitamin A deficiency, Sorsby's fundus dystrophy, autosomaldominant late-onset degeneration, rod-cone dystrophies, color blindness,ocular tumors, cataract, diabetic retinopathy, and glaucoma.

The improved photobleaching methods described may be used in a varietyof protocols, as would be obvious to one of ordinary skill in the art.As such, the exact protocol used with the described photobleachingmethods may be varied as is known in the art. The goal of thephotobleaching procedure in a psychophysical test (such as, but notlimited to, dark adaptation) is to precondition the test eye of asubject, or portions thereof, by desensitizing at least a portion of thevisual pigments of the test eye through exposure to a photobleachinglight. In dark adaptation, for example, visual recovery of scotopicvision is then measured as the test eye adapts to a second light (oftenreferred to as the target or target stimulus). Therefore, thephotobleaching light serves as a standardized baseline from which visualrecovery is measured. Therefore, the photobleaching step is ofimportance to psychophysical tests since it plays a role in establishinga baseline for the tests. Furthermore, depending on the nature of thephotobleaching method used, the time required to complete thepsychophysical test, the patient burden and patient discomfort, and thereproducibility and/or accuracy of the psychophysical test may beimpacted.

In one embodiment for dark adaptation, the photobleaching light has agreater intensity than the target stimulus, but the absolute intensityvalues of the photobleaching light and the target stimulus may be variedas desired. Generally, the greater the absolute value of the intensityof the photobleaching light, the shorter the period of exposure of thetest eye to the photobleaching light to achieve the baseline. Forexample, the photobleaching light may be an intense light, such as thatprovided by an electronic strobe or flash, and the light of theintensity of the target stimulus may be at or close to 0 cd/m², such aswould occur in a dark room. Alternatively, the photobleaching light maybe a light produced by an ordinary light bulb or by the ambient light ina room, and the intensity of the target stimulus may be at or close to 0cd/m², such as would occur in a dark room. However, in general, thegreater the intensity of the photobleaching light, the longer thepsychophysical test takes to administer.

The wavelength of light emitted by the photobleaching light may also bevaried. While the prior art methods utilized an achromatic bleachinglight having a broad band spectrum of wavelengths, the presentdisclosure describes photobleaching methods that utilize aphotobleaching light tailored to emit a light of a particular wavelengthor a range of wavelengths of the visible spectrum so that light of onlya particular wavelength or range of wavelengths is used in the bleachingprocess. In one embodiment, the particular wavelength or range ofwavelengths is selected to match the specific absorption spectra of therod, cone and/or retinal ganglion cell photoreceptors. As discussedabove, rods absorb light in a broad band of the spectrum peaking at awavelength of 505 nm, while the three types of cone photoreceptors havespectral responses peaking around 419 nm (S cones), around 531 nm (Mcones), and around 558 nm (L cones) and the retinal ganglion cellsabsorb light having a spectral response peaking around 460 nm.Therefore, in one embodiment, the photobleaching light may be selectedto stimulate one or more of the rod, cone and/or retinal ganglion cellphotoreceptors by utilizing a photobleaching light emitting a wavelengthor a range of wavelengths based on the spectral responses of thephotoreceptors.

The photobleaching light emitting a particular wavelength or range ofwavelengths of light may be generated by an achromatic light sourceequipped with a suitable filter, such as, but not limited to, anarrow-band pass filter, a high pass filter (eliminating lowerwavelengths) or a low pass filter (eliminating the high wavelengths). Avariety of narrow-band pass filters, high pass filters and low passfilters are commercially available and one of ordinary skill in the artwould be well versed in the selection of the appropriate filter based onthe test conducted and the results desired. Alternatively, thephotobleaching light of a particular wavelength or range of wavelengthsmay be generated directly by a source generating the desired wavelengthor wavelengths (such as, but not limited to, light emitting diodes,LEDs, or organic light-emitting diodes, OLEDs).

Many light delivery methods can be used to generate and/or deliver thephotobleaching light. In one embodiment, the photobleaching light isgenerated by a xenon lamp, an arc lamp, a tungsten bulb, a photographicflash, a LED or OLED light source. Other possibilities include the useof display technologies such as cathode ray tubes (CRTs), plasmadisplays and LED displays. Other sources may also be used to generatethe photobleaching light. As discussed above, the light sources may beequipped with filters or other devices to emit and/or generate light ofa specific wavelength or range of wavelengths. The photobleaching lightmay be delivered using a variety of techniques as well, such as but notlimited to, adapting fields, illuminated backgrounds, direct projectioninto the eye, exposure to ambient light, or staring into a light bulb.Classically, subjects viewed an adapting field in photobleachingmethods. This bleaching method causes discomfort to the subject, and itis difficult to reliably deliver bleaches in psychophysicallyinexperienced subjects. Another method of bleaching is to project lightinto the eye using a Maxwellian view system. This method causes lessirritation, but requires the subjects to fixate very steadily and notblink for 30 to 60 seconds. Many inexperienced subjects find this to bea difficult task. If the subject changes fixation or blinks, it isnecessary to wait up to two hours before the bleach is repeated to avoidthe cumulative effects of bleaching. Bleaching light delivered by anelectronic strobe or flash delivers the photobleaching light in a shortperiod of time. In addition, the intensity and/or wavelength or range ofwavelengths emitted by the bleaching light may be easily modulated. Inaddition, the use of masks or similar devices allows the bleaching lightto be of a desirable size and positioned at a desired location. Becausethe light exposure is brief, the intensity and/or wavelength(s) of thephotobleaching light can be controlled and can be localized to a desiredarea, the photobleaching light is not irritating to the subjects and thesubjects do not need to maintain fixation for a long period of time.With proper patient instructions blinking is not an issue.

The photobleaching light may be delivered to a desired portion of theretina. Using the delivery methods described above, it is possible todeliver the photobleaching light to a single discrete area of the retinaor to more than one discrete area of the retina during a single test. Byselecting a particular area or areas of the retina to be bleached by thephotobleaching light, patient discomfort can be minimized by avoidingsensitive areas of the eye such as the fovea. In addition, depending onthe goal of the test to be administered, a specific region of the retinamay be selected for photobleaching. For example, when administering apsychophysical test for dark adaptation or other rod mediated function,it is not required to bleach the fovea since there are no rodphotoreceptors in the fovea. Therefore, photobleaching a desired area orareas of the retina outside the fovea is advantageous. Finally, byphotobleaching more than one discrete area of the retina, not only arethe above mentioned advantages obtained, but in addition, differentareas of the retina may be tested simultaneously to monitor diseaseprogression and/or to get differential measurements from areas having orsuspected of having greater or lesser dysfunction or to increase thestatistical accuracy of the test results by providing more than onereading.

As discussed above, the photobleaching protocol desensitizes the desiredamount of visual pigment in the rod, cone and/or retinal ganglion cellphotoreceptors by exposure to a photobleaching light and provides astandardized baseline to measure visual recovery. The intensity of thephotobleaching light, the time of exposure to the photobleaching lightand/or the wavelength(s) of the photobleaching light can be modulated toproduce the desired amount of desensitization as described herein. Inone embodiment, an equivalent of about 50% to 100% of the visual pigmentin the area subject to photobleaching is desensitized. The intensity ofthe photobleaching light can be adjusted to desensitize the appropriateamount of visual pigment in the area subject to photobleaching. Forexample, a photobleaching light intensity of 748 log scot Td sec⁻¹ willbleach approximately 98% of the rhodopsin molecules, while aphotobleaching light intensity of 5.36 log scot Td sec⁻¹ will bleachapproximately 50% of the rhodopsin molecules. Alternate photobleachinglight intensities which desensitize less than 50% or more than 50% ofthe rhodopsin (or other visual pigment) molecules may also be used ifdesired.

After the bleaching protocol, visual recovery is monitored. In darkadaptation, for example, this recovery is mediated primarily by theretina and measures predominately rod-mediated scotopic sensitivity.Although many methods to monitor rod-mediated scotopic sensitivity areknown, generally, the subject provides a series of responses to a targetstimulus (which is varied in intensity, location and/or wavelength asdescribed herein). In one method, the response of the subject is used todetermine a threshold measurement. During threshold measurements, thesubject is presented with a target stimulus. The target stimulus may bea spot of light, including a light spot on a darker background or a darkspot on a lighter background. Subjects may view the target stimulus withor without their best optical correction for the test distance. Avariety of classical methods can be used to determine the thresholdmeasurement, including but not limited to method of limits, justnoticeable difference, and method of adjustment. These techniques arewell known in the art. Thresholds measurements can be sampled in such away as to provide sufficient data to fit models of dark adaptation. Inone embodiment, threshold measurements are sampled once every 1 to 5minutes. Another embodiment would be to sample threshold measurementstwice every minute. Yet another embodiment would be to sample 2threshold measurements per minute early during the test then sample 1threshold measurement every 2 minutes thereafter. Higher or lowersampling rates may be used as desired to balance the need of producingan adequate dark adaptation function for model fitting against subjectburden. As an example of lower sampling rates, a small number ofthreshold measurements may be sampled based on predictions of rodphotoreceptor function in normal individuals. For example, a thresholdmeasurement may be obtained at 3-5 minutes (which using classicalphotobleaching and target stimulus parameters in normal individualswould be before the rod-cone break) and at 5-10 minutes and 10-15minutes. If these threshold measurements do not correlate with the rodphotoreceptor function in normal individuals, the subject is likely tohave impaired dark adaptation. Such a sampling schedule would furtherreduce subject burden. Additional description of methods and apparatusused in photobleaching methods and methods of analysis for determiningthe dark adaptation status of a patient are described in U.S. patentapplication Ser. No. 10/571,230, which is hereby incorporated byreference.

Description of Specific Embodiments

In one embodiment of the photobleaching method described herein, thephotobleaching light is tailored to emit a spectrum consistingessentially of a selected wavelength or range of wavelengths of lightrather than an achromatic photobleaching light having a broad range ofwavelengths. In many psychophysical tests, such as, but not limited to,dark adaptation, it may be advantageous to choose a photobleaching lighttailored to emit a spectrum consisting essentially of a desiredwavelength or a range of wavelengths that reveal the rod-mediatedscotopic sensitivity as quickly as possible. Alternatively, it may beadvantageous to choose a photobleaching light tailored to emit aspectrum consisting essentially of a desired wavelength or a range ofwavelengths that provides a clearly visible rod-cone break as acharacteristic benchmark for dark adaptation.

In a particular embodiment, the photobleaching light tailored to emit aspectrum consisting essentially of a desired wavelength or a range ofwavelengths selected to preferentially photobleach the rodphotoreceptors, the cone photoreceptors and/or retinal ganglion cells.For example, the photobleaching light may be selected to preferentiallybleach the rod photoreceptors. In such an example, the photobleachinglight would emit a spectrum consisting essentially of a wavelength oflight of 505 nm or a range of wavelengths of light centered on 505 nm.As used herein, the term “centered” on a particular wavelength means thephotobleaching light contains the particular wavelength of light and arange of other wavelengths of light from 5 to 20 nm on either side ofthe particular wavelength; the term centered should not be interpretedto mean the range of wavelengths is symmetrical about the particularwavelength. In the above example, light consisting essentially of arange of wavelengths centered on 505 nm could include, for example,wavelengths of light from 490 to 520 nm (15 nm on either side of 505nm), from 490 to 510 nm, or from 490 to 525 nm. In another example, thephotobleaching light may be selected to preferentially bleach the Scones photoreceptors. In such an example, the photobleaching light wouldemit a spectrum consisting essentially of a wavelength of light of 419nm or a range of wavelengths of light centered on 419 nm. In yet anotherexample, the photobleaching light may be selected to preferentiallybleach the M and. L cone photoreceptors while leaving the rodphotoreceptors relatively unaffected. In such an example, thephotobleaching light would emit a spectrum consisting essentially of awavelength of light of 650 nm or a range of wavelengths of lightcentered on 650 nm, or alternately a broad range of wavelengths of lightfrom about 600 nm to about 700 nm.

Other embodiments may also be envisioned. For example, when desired topreferentially bleach the visual pigment in the retinal ganglion cells,the photobleaching light may be tailored to emit a spectrum consistingessentially of a wavelength of light of 460 nm or a range of wavelengthsof light centered on 460 nm, such as but not limited to, about 450 toabout 470 nm.

In a further example, the photobleaching light may be tailored to emit aspectrum consisting essentially of a wavelength of light or a range ofwavelengths of light over about 480 nm. Such a spectrum ofphotobleaching light may be used to exclude wavelengths of light in theblue spectra to reduce variability and confounding effects introduced bylens opacity.

In yet another example, the photobleaching light may be tailored to emita spectrum consisting essentially of a wavelength of light of about 410nm or centered on 410 nm, such as but not limited to a range of about400 to about 420 nm. Such a spectrum of photobleaching light may be usedto maximize absorption due to lens opacity.

In still a further example, the photobleaching light may be tailored toemit a spectrum consisting essentially of a wavelength of light of about570 nm or centered on 570 nm, such as but not limited to a range ofabout 560 to about 580 nm. Such a spectrum of photobleaching light maybe used to minimize absorption due to lens opacity.

In yet another example, when a target stimulus is used, thephotobleaching light may be tailored to emit a spectrum that matches thespectrum of the target stimulus. When it is desired to accentuate therod response, the spectrum of the photobleaching light and the targetstimulus may be tailored to emit a spectrum consisting essentially of awavelength of light of about 500 nm or centered on 500 nm, such as butnot limited to a range of about 490 to about 510 nm. When it is desiredto accentuate the cone response, the spectrum of the photobleachinglight and the target stimulus may be tailored to emit a spectrumconsisting essentially of a wavelength of light of about 650 nm orcentered on 650 nm, such as but not limited to a range of about 640 toabout 660 nm. In a further variation, the photobleaching light may betailored to emit a spectrum that does not match the spectrum of thetarget stimulus.

In one version of this embodiment, rather than utilizing an achromaticor broadband bleaching light, a dark adaptometer can be configured topreferentially photobleach the rods. This could be accomplished, forexample, by placing a band pass filter narrowly centered on 505 nm overa broadband xenon arc flash or other light source and using theresulting narrow spectrum emitted light as the bleaching source.Alternatively, the bleaching light could be configured to preferentiallyphotobleach rods by constructing a bank of one or more light-emittingdiodes (LEDs), organic light-emitting diodes (OLEDs) or other lightsource of a single type having a characteristic emission spectrum closeto 505 nm. Other possibilities include the use of display technologiessuch as cathode ray tubes (CRTs), plasma displays and LED displays.Utilizing a bleaching spectrum that is tailored to preferentiallyphotobleach the rods offers several advantages. Therefore, thephotobleaching light is tailored to emit a light consisting essentiallyof a desired wavelength or range of wavelengths of light.

As discussed above, the photobleaching light emitting a desiredwavelength or spectrum of wavelengths may be generated using a varietyof methods. For example, a light source equipped with a suitable filter,such as, but not limited to, a narrow-band pass filter, a high passfilter (eliminating lower wavelengths) or a low pass filter (eliminatingthe high wavelengths). A variety of narrow-band pass filters, high passfilters and low pass filters are commercially available and one ofordinary skill in the art would be well versed in the selection of theappropriate filter based on the test conducted and the results desired.Alternatively, the photobleaching light of a particular wavelength orrange of wavelengths may be generated directly by a source generatingthe desired wavelength or wavelengths (such as, but not limited to,light emitting diodes, LEDs, or organic light-emitting diodes, OLEDs).

Using a photobleaching method incorporating a photobleaching lighttailored to emit a desired wavelength or range of wavelengths hasseveral advantages. A first advantage is the ability to administer apsychophysical test, such as, but not limited to, dark adaptation, in adecreased amount of time, thereby increasing the efficiency of the testoperator and minimizing patient burden. When an achromatic or broadbandbleaching light is utilized in a photobleaching method, all of thephotoreceptors, both rod and cone, are strongly bleached. Cones recovermore rapidly than rods. Nevertheless, during the initial post-bleachperiod the sensitivity threshold is still dominated by the conerecovery, and the important rod-mediated scotopic sensitivity recoveryinformation is obscured. However, using a photobleaching methodincorporating a photobl caching light tailored to emit a desiredwavelength or range of wavelengths can minimize the bleaching ofphotoreceptors whose function is not being tested. For example, using ableaching light consisting essentially of a wavelength of light of 505nm or centered on 505 nm, the photobleaching of the three conephotoreceptors is minimized and they are only weakly photobleached. As aresult, the cones recover more rapidly, and the important rod-mediatedscotopic sensitivity recovery information is more quickly revealed (seeFIG. 2.) FIG. 2A is a theoretical illustration of a dark adaptationcurve for a normal individual obtained using a broad, achromaticphotobleaching light and a 505 nm stimulus target. Cone recovery and rodrecovery are both exponential. Scotopic sensitivity is cone-mediateduntil the cone recovery plateaus to reveal the ultimately more sensitiverod-mediated response. FIG. 2B is a theoretical illustration of a darkadaptation curve for a normal individual obtained using a photobleachinglight emitting a range of wavelengths centered on 505 nm and a targetstimulus of 505. The cone recovery reaches its plateau essentiallyinstantaneously and the rod recovery is more rapid than for theconditions of FIG. 2A, more quickly reaching the rod-cone break andrevealing the subsequent rod-mediated recovery.

A second advantage is reduced patient burden during the test. Visualdiscomfort from bright lights is mainly associated with the shortwavelength portion of the visible spectrum. As illustrated in Example 2,using a photobleaching light having a wavelength of 505 nm or a spectrumof wavelengths centered on 505 nm reduces patient burden by eliminatingthe most irritating short wavelength components of the light.Furthermore, the cone photobleaching associated with an achromatic orbroadband photobleaching light creates a more persistent after image,which in turn causes the light of the target stimulus to be less salientand makes the test more difficult for the patient.

A third advantage is reduced measurement bias due to variation in thelens opacity of the patient. With aging or in the event of cataracts,the lens in the eye becomes more opaque and preferentially absorbs lightat short wavelengths (i.e., 480 nm and below). With an achromatic orbroadband bleaching light that contains a significant short wavelengthcomponent, variable lens density between otherwise similar subjectscauses variability in the photobleaching achieved, and in turn anartificial variability in the measured dark adaptation. By using aphotobleaching light tailored to emit a desired wavelength or spectrumof wavelengths that do not contain the shorter wavelengths, suchvariability is reduced.

Using a photobleaching method incorporating a narrow-band passphotobleaching light other than 505 nm or a range of wavelengthscentered on 505 nm will minimize or maximize the degree of the abovedescribed advantages, depending on the wavelength or range ofwavelengths chosen. In addition, at least some of the advantagesdescribed above (such as lowered patient burden and reduced bias due tolens opacity) can be obtained by use of a high pass filter to eliminatethe short wavelength portion of the photobleaching spectrum rather thana narrow-band pass filter, although a narrow-band pass filter may alsobe used.

In yet another embodiment, further advantage may also be obtained usinga photobleaching method utilizing a photobleaching light tailored toemit a desired wavelength or spectrum of wavelengths selected tocomplement a target stimulus of a specific wavelength(s) of light. Forexample, by combining a photobleaching light consisting essentially of awavelength of light of 560 nm or a range of wavelengths of lightcentered on 560 nm with a target stimulus consisting essentially of awavelength of light of 450 nm or a range of wavelengths of lightcentered on 450 nm, it is possible to obtain a rapid assessment of therod-mediated scotopic sensitivity recovery (i.e., dark adaptation). Sucha photobleaching light will only weakly photobleach the S cones, butwill strongly photobleach the M and L cones as well as the rods.Conversely, all of the S, M and L cones as well the rods are stronglyresponsive to such a target stimulus. Given this combination, during theinitial portion of the rod-mediated scotopic sensitivity recovery the Scone response will dominate the M and L cone responses, and rapidlysaturate at the short wavelength cone plateau until the ultimately moresensitive rods take over. This provides a clear rod-cone break (thepoint at which sensitivity recovery transitions from being conedominated to being rod dominated) in the threshold curve. Anillustration is provided in FIGS. 3A and B. FIG. 3A is a theoreticalillustration of a dark adaptation curve for a normal individual obtainedusing a broad, achromatic bleaching light and a 505 nm target stimulus.Cone recovery and rod recovery are both exponential. Scotopicsensitivity is cone-mediated until the cone recovery plateaus to revealthe ultimately more sensitive rod-mediated response. FIG. 3B is atheoretical illustration of a dark adaptation curve for a normalindividual obtained using a photobleaching light emitting a range ofwavelengths centered on 560 nm and a stimulus target centered on 450 nm.The cone recovery plateaus at a higher level and the rod recovery ismore rapid than for the conditions of FIG. 3A, more quickly reaching therod-cone break and revealing the subsequent rod-mediated recovery.

In an alternate embodiment of the photobleaching method describedherein, the bleaching light is restricted to a portion of the retina sothat only a portion of the retina is photobleached. The area of theretina to be photobleached may be selected based on the particular testto be administered, the results desired, or the nature of thephotoreceptors desired to be photobleached; furthermore, the area of theretina to be photobleached may be selected in order to maximizediagnostic sensitivity for a particular disease and/or to minimizepatient burden. A combination of the above factors may also suggestcertain portions of the retina to be photobleached. The positioning ofthe bleaching light to a desired area of the retina can be accomplished,for example, by an appropriately located and sized mask over thebleaching light or the bleaching light could be projected onto only thedesired region of the retina. In addition, a fixation light or otherelement and/or a restraint, such as, but not limited to, a chin rest orbite bar, could be used in combination with the foregoing to orient thepatient's retina to allow precise placement of the bleaching light on adesired portion of the retina.

In a particular embodiment, in a psychophysical test for darkadaptation, it may be beneficial to restrict application of thebleaching light to an area of the parafovea and avoid application of thebleaching light to the fovea. Application of the bleaching light to thefovea causes greater irritation than light directed at regions of theretina outside the fovea, such as, but not limited to, the parafovea.Furthermore, there are no rod photoreceptors in the fovea, so bleachingthe fovea will not contribute to assessment of rod-mediated function.

In addition, some diseases that are associated with impaired darkadaptation exhibit greater or lesser impairment depending on the regionof the retina tested. In the case of age-related macular degeneration,for example, AMD-related impairment of the rods is greatest near thefovea and decreases as a function of eccentricity towards the peripheralretina. It is therefore possible to monitor disease progression bydetermining the patient's dark adaptation status at several points ofthe retina as a function of eccentricity towards the peripheral retina.Therefore, by selectively photobleaching only desired areas of theretina with different degrees of eccentricity, the progression ofcertain diseases can be monitored. In such embodiments, several areas ofthe retina with different degrees of eccentricity can be photobleachedat one time, with the patient's dark adaptation status being determinedfor each region of the retina that is photobleached, for example byinterleaving threshold measures at the multiple regions. As is obvious,the different regions of the retina could also be studied independentlyin completely separate tests.

In a particular embodiment suitable for the testing of dark adaptation,the region of the retina that is photobleached is restricted to a smallfocal area equal to 4° of visual field centered at 5 in the inferiorvisual field (in the macula but outside the fovea), with this beachingregion being only moderately larger than the target stimulus light spot.This choice of bleaching region offers several advantages. For one,patient burden is minimized, both because the fraction of the retinabeing photobleached is small and because the region selected excludesthe fovea, which is the portion of the retina most susceptible toirritation. Avoiding the fovea also allows the patient to maintainfixation easier during the test, which is critical for test reliability.For another, diagnostic sensitivity for AMD is optimized, becauseAMD-related impairment of dark adaptation is greatest in this region ofthe retina.

In other embodiments, the photobleaching light photobleaches a portionof the retina as set forth below.

In one example, the portion of the retina exposed to the photobleachinglight is an area of the fovea, an area of the parafovea or a combinationof the foregoing. The portion of the retina exposed to thephotobleaching light may be located entirely inside the fovea (at about0° to about 0.5° eccentricity). Such localization would allowphotobleaching primarily of the cone photoreceptors and may be useful insuch psychophysical tests as color sensitivity or color discrimination.The portion of the retina exposed to the photobleaching light may belocated entirely inside the macula (at about 2° to about 10°eccentricity or at about 3° to about 10° eccentricity). Suchlocalization would allow photobleaching primarily of the rodphotoreceptors and may be useful in such psychophysical tests as darkadaptation. Furthermore, the portion of the retina exposed to thephotobleaching light may be located in the peripheral retina (at about10° to about 30° eccentricity), Such localization may be useful in suchpsychophysical tests as visual field or perimetry.

In another example, the portion of the retina exposed to thephotobleaching light may be an annular region completely excluding thefovea. In a specific example, the annular region may have an inner edgelocated at or outside about 2° eccentricity and an outer edge located ator inside about 10° eccentricity. Such localization would allowprimarily bleaching of the rod photoreceptors as discussed above.

In a further example, the portion of the retina exposed to thephotobleaching light covers an area of about 4° of visual field to about6° of visual field. Such an area allows a minimum effective area of theretina to be exposed to photobleaching while providing a photobleachedarea that can be effectively exposed to the target stimulus. In anotherexample, the portion of the retina exposed to the photobleaching lightis co-located with the portion of the retina exposed to the targetstimulus and the portion of the retina exposed to the bleaching lightbeing from about 1 to about 4 times the area of the portion of theretinal exposed to the target stimulus. In a specific example, theportion of the retina exposed to the photobleaching light is about 3times the area of the portion of the retinal exposed to the targetstimulus.

In still a further example, the portion of the retina exposed to thephotobleaching light is located on the inferior vertical meridian or thesuperior vertical meridian. Such localization allows for symmetrybetween the right and left eye.

In yet another example, the portion of the retina exposed to thephotobleaching light has a distinctive shape. In certain cases, thephotobleaching process may produce an after image. When a targetstimulus is used, such as in conjunction with a psychophysical test, thesubject may confuse the after image with the target stimulus. Byproviding a distinctive shape to the photobleaching light such confusionis minimized. The shape may be a circle, a square, a triangle, adiamond, a polygon, a star or other shape as desired. in a specificexample, the photobleaching light and the target stimulus have differentshapes. If desired, color may be substituted for shape, or both colorand shape may be used.

In yet another alternate embodiment of the photobleaching methoddescribed herein, the photobleaching method utilizes a bleaching lightwith an intensity that is at or below the intensity of ambient daylightlevels. For the purpose of this disclosure, the intensity of ambientdaylight is in the range of 50 to 400 cd/m² or 3.15 to 4.05 log scot Tdsec⁻¹. Prior photobleaching methods and devices utilizing such methods,especially those used for measuring dark adaptation, utilized aphotobleaching light having an intensity that was well above theintensity of ambient daylight. This brute force approach was used toensure a uniform state of photobleaching, or adaptation starting point,for all patients. However, it is also possible to ensure a uniform stateof photobleaching with a photobleaching light having an intensity thatis at or below the intensity of ambient daylight. For example, thepatient can be taken from ambient daylight into a dark room, allowed todark adapt briefly to a level below ambient daylight, and thenphotobleached using a flash of light having an intensity at or below theintensity of ambient daylight. Alternatively, the patient can be takenfrom ambient daylight into a dark room, exposed to a steadyphotobleaching light having an intensity below the intensity of ambientdaylight until such time as the steady photobleaching light is clearlyvisible to the patient, thus effectively arresting dark adaptation forall patients at a common starting level below ambient daylightconditions. In the latter alternative, the steady photobleaching lightcan be a randomly selected shape that the patient must identify to thetest operator before dark adaptation testing can proceed, therebyverifying that the patient is appropriately pre-conditioned. Use of aphotobleaching light with an intensity that is at or below the intensityof ambient daylight levels offers several advantages. In particular, thepatient burden is reduced. In addition, as illustrated in Example 4below, the overall dark adaptation test time can be shortened.

The described photobleaching methods may utilize one, two or all threeof the above described improvements, in any combination. For example, aphotobleaching method may be provided using a photobleaching lightemitting a light consisting essentially of a specific wavelength oflight or a tailored spectrum of wavelengths centered on a specificwavelength of light. In another example, a photobleaching method may beprovided using a photobleaching light emitting a light consistingessentially of a specific wavelength of light or a tailored spectrum ofwavelengths centered on a specific wavelength of light in combinationwith only a particular area of the retina photobleached. In yet anotherexample, a photobleaching method may be provided using a photobleachinglight having an intensity that is at or below the intensity of ambientdaylight.

Furthermore, the described photobleaching methods may also beincorproated into an apparatus, machine or device used to administer apsychophysical test that requires photobleaching, such as, but notlimited to a dark adaptometer. Such apparatus, machines or devices arewell known in the art and may be modified to incorporate thephotobleaching methods described herein. Such a modified apparatus,machine or device is also within the scope of the present disclosure.For example, the dark adaptometer disclosed in U.S. Pat. No. 10/571,230could be modified to incorporate the photobleaching methods describedherein. Likewise, a photobleaching light source capable of emitting atailored range of wavelengths or a particular wavelength suitable tophotobleach a desired population of rod, cone or ganglion cellphotoreceptors or a photobleaching light emitting a light having anintensity at or below the intensity of ambient daylight are also withinthe scope of the disclosure, as well as the use of such photobleachinglight sources in an apparatus, machine or device used to administer apsychophysical test that requires photobleaching.

The present disclosure also provides a combination of a photobleachinglight as described herein and an apparatus to administer apsychophysical test to monitor a response to the photobleaching light.The photobleaching light may be a part of the apparatus. As discussedabove, the nature of the apparatus may be determined by thepsychophysical test administered. For example, dark adaptometers (orbiophotometers) are used to measure dark adaptation and diagnoseage-related macular degeneration, preferential hyperacuity perimetersare used to measure Vernier acuity and assess the severity ofage-related macular degeneration, ETDRS charts are used to measurespatial resolution acuity, Pelli-Robson contrast sensitivity charts areused to measure contrast sensitivity, the Farnsworth-Munsell 100 HueTest is used to measure color vision, frequency doubling perimeters areused to measure frequency doubling visual illusion, and field analyzersare used to measure visual field and diagnose glaucoma.

An exemplary apparatus combination is shown in FIGS. 9A and 9B. Theapparatus combination 1 (i.e., a dark adaptometer) comprises a housing10. The housing 10 has a viewing opening 50 to receive the head of thesubject being tested. The housing 10 contains the basic components ofthe apparatus combination 1, including in particular a photobleachingapparatus 40 for photobleaching a restricted region of a retina of asubject's eye and a stimulus apparatus 20 for exposing a desired portionof a retina of a subject's eye to a target stimulus light.

In one embodiment, the photobleaching apparatus 40 includes a bleachinglight source 41 (for example one of more LEDs) to generate a bleachinglight beam 42. The bleaching light source 41 may be adjusted to providea high intensity or a low intensity beam. The bleaching light beam 42 isacted on by one or more optical elements, including for example shapingoptics 45 to collimate and shape the beam (for example a mask with anappropriately sized aperture or a series of lenses), an optical filter46 to select the desired spectrum of the beam 42, and a directing means44 (for example a mirror) to direct the beam to a display 34 (forexample a screen). These elements combine to produce a bleaching spot 48(FIG. 9B) of the desired size, shape and spectrum of light on thedisplay 34 to photobleach at least a portion of rod visual pigment inonly a restricted region of a retina of the subject's eye.

In one embodiment, the stimulus apparatus 20 includes a stimulus lightsource 21 (for example one or more LEDs) to generate a stimulus lightbeam 22. The stimulus light source 21 may be adjusted to control theintensity of the stimulus light bean 22 over a broad dynamic range. Thestimulus light source 21 is acted one by one or more optical elements,including for example shaping optics 25 to collimate and shape the beam(for example a mask with an appropriately sized aperture or a series oflenses), an optical filter 26 to select the desired spectrum of the beam22, and a directing means 24 (for example a mirror) to direct the beamto the display 34 (for example a screen). These elements combine toproduce a target stimulus spot 28 (FIG. 9B) of the desired size, shapeand spectrum of light on the display means 34 so that only a portion ofa retina of the subject's eye is exposed to the target stimulus.

Psychophysical tests using visual stimuli include, for example, darkadaptometry, visual sensitivity tests, spatial resolution acuity tests,contrast sensitivity tests, flicker photometry, photostress tests,Vernier acuity tests, colorimetry, motion detection tests, objectrecognition, and perimetry. The combination can be used to assess thestatus of visual functions including, for example, dark adaptation,photopic sensitivity, scotopic sensitivity, visual acuity, colorsensitivity, contrast sensitivity, color discrimination, and visualfield. Furthermore, the combiantion can be used to diagnosis the risk,presence or severity of eye diseases including, for example, age-relatedmacular degeneration, vitamin A deficiency, Sorsby's fundus dystrophy,autosomal dominant late-onset degeneration, rod-cone dystrophies, colorblindness, ocular tumors, cataract, diabetic retinopathy, and glaucoma.

EXAMPLES Example 1 Effect of Photobleaching Light Spectrum on the Shapeand Kinetics of Dark Adaptation Curves

In this example, a comparison was made between dark adaptation curvesgenerated using a photobleaching light emitting an achromatic whitelight comprising a broad spectrum of wavelengths and dark adaptationcurves generated using a photobleaching light emitting a tailoredspectrum of wavelengths centered on only the blue, green and redportions of the achromatic white photobleaching light.

Dark adaptation was measured using an AdaptDx dark adaptometer(Apeliotus Technologies, Inc.) according to the manufacturer'sinstructions, using methods known in the art. The intensity of the xenonarc photobleaching light (administered as a flash) incorporated in thedark adaptometer was set at 7.03 log scot Td sec⁻¹ and masked tophotobleach an area of the retina covering about 4° of visual anglecentered at 6° on the inferior vertical meridian. The spectrum of thephotobleaching light was varied for each of four dark adaptationmeasurements. In one case, the photobleaching light emitted theessentially white, 5500 Kelvin color temperature broad spectrum light(consisting of wavelengths from about 400 nm to about 700 nm) generatedby the xenon arc source (FIG. 4A). In the other three cases, thephotobleaching light was tailored to emit a spectrum of light consistingessentially of wavelengths in the narrow blue (about 405 nm to about 425nm), green (about 490 nm to about 510 nm) and narrow red (about 640 nmto about 660 nm) spectrums (FIGS. 4B-D, respectively). As used in thepresent the disclosure, the term “about” when used in reference to awavelength or range of wavelengths it is meant to encompass a range ofwavelengths on either side of the designated wavelength equal to theerror in generation or measurement of the designated wavelength. Thespectrums detailed above were generated by placing narrow bandpassinterference filters (Edmund Optics NT43-158, NT43-169 and. NT43-189,respectively) over the face of the xenon arc flash window. The test eyewas photobleached while the subject was focused on a fixation light toensure that the proper retinal location was bleached. Scotopic thresholdmeasurements for the target stimulus began immediately after photobleachoffset. The target stimulus was a circular spot covering about 2° ofvisual angle presented at 6° on the inferior vertical meridian with awavelength spectrum centered on 500 nm. During threshold measurement thesubject focused on the fixation light and responded when the stimuluswas judged to be present by pushing a button. Threshold was estimatedusing a 3-down/1-up modified staircase procedure. Starting at arelatively high intensity (5.00 cd/m²), the target was presented every 2or 3 seconds for a 200-ms duration. If the subject did not respond thetarget stimulus was visible, the intensity of the target stimulusremained unchanged until the subject responded the target stimulus wasvisible. If the subject indicated the target stimulus was visible, theintensity of the target stimulus was decreased for each successivepresentation in steps of 0.3 log units (“3-down”) until the participantstopped responding that the target stimulus was present. After thesubject indicated that the target stimulus was invisible by not pushingthe button, the intensity of the target stimulus was increased for eachsuccessive presentation in steps of 0.1 log units (“1-up”) until thesubject responded that the target stimulus was once again visible. Thisintensity was defined as the threshold estimate. Successive thresholdmeasurements were obtained starting with a target stimulus intensity 0.3log units brighter than the previous threshold estimate. The subject hada 30-second rest period between threshold measurements. Thresholdestimates were made about once a minute for the duration of themeasurement protocol. About twenty threshold measurements were madeduring each dark adaptation test.

FIGS. 4A-D show four dark adaptation curves from the same test subjectgenerated in response to the four different photobleaching lightspectrums described above. The subject shows a stereotypical darkadaptation curve in response to the white photobleaching light asexpected (FIG. 4A). Use of a photobleaching light tailored to emit aspectrum of light consisting essentially of wavelengths in the range ofabout 490 nm to about 510 nm (green spectrum), preserves thestereotypical shape of the dark adaptation function because the rods arestill strongly bleached. In contrast, use of a photobleaching lighttailored to emit a spectrum of light consisting essentially ofwavelengths in the range of about 405 nm to about 425 nm (blue spectrum)(FIG. 4C) or a photobleaching light tailored to emit a spectrum of lightconsisting essentially of wavelengths in the range of about 640 nm toabout 660 nm (red spectrum) (FIG. 4D) failed to produce a. stereotypicaldark adaptation response curve because the rods were only weaklyphotobleached. In addition, the dark adaptation response obtained usinga photobleaching light tailored to emit a spectrum of light consistingessentially of wavelengths in the range of about 490 nm to about 510 nm(green spectrum) gave results more quickly than using a photobleachinglight emitting a broad spectrum of light (compare FIGS. 4A and 4B).Recovery occurs faster because the additional photobleachingcontribution from the blue and red components of the white spectrum,which is largely outside the rod response spectrum, has been eliminated.

Therefore, the use of a photobleaching light emitting a tailoredspectrum of light consisting essentially of wavelengths in the range ofabout 490 nm to about 510 nm (green spectrum) was shown to giveessentially the same dark adaptation response as a photobleaching lightemitting a broad achromatic white bleach and to provide the results morequickly. This example shows that, for this particular objective(measuring dark adaptation), a photobleaching light emitting a tailoredspectrum of light consisting essentially of wavelengths in the range ofabout 490 nm to about 510 nm (green spectrum) is an improvement over aphotobleaching light emitting an achromatic broad spectrum of whitelight. However, it should be noted that for other objectives, the use aphotobleaching light emitting a tailored spectrum of wavelengths otherthan. that shown in this example may also be useful. In summary,essentially the same dark adaptation response is obtained with lesspatient burden, both because only a fraction of the total energyimpinges on the retina and because the most irritating short wavelengthportion of the spectrum is eliminated (i.e., the blue spectrum).Moreover, the result is obtained more quickly.

Example #2 Preference Test for White Flash vs. Green Flash

In this example, a preference test was conducted comparing aphotobleaching light comprising a broad wavelength spectrum of about 400nm to about 700 nm generated by a xenon arc light and a photobleachinglight that was tailored to emit a spectrum of light consistingessentially of wavelengths of about 490 nm to about 510 nm (green.spectrum). These photobleaching light spectra were analyzed for theirability to generate classical dark adaptation curves in Example 1 aboveand shown to produce generally similar dark adaptation curves. Thephotobleaching light in each case was generated using a commercialcamera flash system (SunPak 622 Super Pro). This system uses a xenon arclight source that generates a broad, relatively flat spectrum of light(5500 Kelvin color temperature) spanning the entire range of cone androd sensitivity (about 400 nm to about 700 nm). The flash was set at itsmaximum intensity of 7.48 log scot Td sec⁻¹. The “green” flash wascreated by placing a narrow (about 490 nm to about 510 nm) bandpassinterference filter (Edmund Optics; NT43-169) over the face of the xenonarc flash window. The broad wavelength “white” spectrum photobleachinglight was created by placing a clear glass blank (essentially 100%transmittance at all wavelengths) over the face of the xenon arc flashwindow, so that the test subjects were confronted with similarconfigurations in both cases.

For each participant, one eye was exposed to the “white” photobleachinglight comprising a broad wavelength spectrum of about 400 nm to about700 nm and the opposite eye was exposed to the “green” photobleachinglight that was tailored to emit a spectrum of light consistingessentially of wavelengths of about 490 nm to about 510 nm. The flashunit was held approximately 20 cm in front of the test eye, with thenon-test eye covered. The right eye was always exposed to thephotobleaching light first; however, the tests were counterbalanced withregard to sequence, alternating between the first flash being “white”photobleaching light with the properties described above and the firstflash being “green” photobleaching light with the properties describedabove. There was an interval of approximately 1 minute between the twoflashes. Immediately after exposure to each of the “white” and “green”photobleaching lights, the participants were asked to rate discomfort ona scale of 1 to 10, with 1 being “no discomfort, I would look at it allday” and 10 being “highly uncomfortable, I would not want to look at itagain”. At the conclusion of the entire sequence, the participants wereasked if they had to be exposed to one of the “white” or “green”photobleaching lights again which of the two they would prefer.

A total of eleven naïve participants were tested. There were six femalesand five males, all Caucasian, with a mean age of 30.6 years (range 22to 47). The age distributions (mean and range) for the two sexes werecomparable. The results are shown in FIG. 5. There was a clearpreference for the “green” photobleaching light, with an average ratingof 2.8 for the “green” photobleaching light (range 1 to 5) vs. 5.1 forthe “white” photobleaching light (range 2 to 8), and 91% of the subjectsindicated a preference for the “green” photobleaching light if they wereto be tested again. While the subpopulation numbers are small, there wasa consistent preference for the “green” photobleaching light regardlessof sex, age (under 30 vs. over 30) or the order of the “white”-“green”photobleaching light sequence. There was a tendency for young females tobe more sensitive to the “white” photobleaching light and to show astronger preference for the “green” photobleaching light.

Example 3 Effect of Photobleaching Light Spectrum on Variability in DarkAdaptation Measurements Due to Lens Opacity

In this example, a comparison was made between dark adaptation curvesgenerated using a photobleaching light that was tailored to emit aspectrum of light consisting essentially of wavelengths of about 490 nmto about 510 nm (green spectrum) and a photobleaching light that wastailored to emit a spectrum of light consisting essentially ofwavelengths of about 440 nm to about 460 nm (blue spectrum), both withand without a blue absorption filter in front of the test subject's eye.The blue absorption filter simulates the preferential absorption ofshorter wavelengths due to lens opacity.

Dark adaptation functions were measured using an AdaptDx darkadaptometer (Apeliotus Technologies, Inc.) as described in Example 1above as modified below. To generate the photobleaching light with thegreen spectrum, the intensity of the xenon arc light source incorporatedin the dark adaptometer was set at 7.03 log scot Td sec⁻¹, and a narrowgreen (about 490 nm to about 510 nm) bandpass interference filter(Edmund Optics NT43-169) was placed over the face of the xenon arc flashwindow. To generate the photobleaching light with the blue spectrum, theintensity of the xenon arc light source incorporated in the darkadaptometer was set at 7.60 log scot Td sec⁻¹, and a narrow blue (about440 nm to about 460 nm) bandpass interference filter (Edmund OpticsNT43-163) was placed over the face of the xenon arc flash window. FIGS.6A-D show the resulting dark adaptation functions. Placing the blueabsorption filter in front of the test subject's eye to lower thetransmission of short-wavelength light in a fashion similar to thatencountered with lens opacity, such as caused by cataracts andage-related increases in lens opacity, had minimal impact on the darkadaptation curves generated using the green spectrum photobleachinglight (compare FIG. 6A, designated control, vs. FIG. 6B, designatedsimulated lens opacity). Conversely, the simulated lens opacity had amajor impact on the dark adaptation curves generated using the bluespectrum photobleaching light (compare FIG. 6C, designated control, vs.FIG. 6D, designated simulated lens opacity).

These results show that the use of a photobleaching light tailored toemit a spectrum of light consisting essentially of wavelengths of about490 nm to about 510 nm (green spectrum) minimizes the variability indark adaptation responses, and associated diagnostic measurements, dueto the filtering effects of lens opacity, such as caused by cataractsand age-related increases in lens opacity.

Example 4 Photobleaching Below Ambient Daylight Levels

In this example, a comparison was made between dark adaptation curvesgenerated using a photobleaching light having an intensity above theintensity of ambient daylight and a photobleaching light having anintensity below the intensity of ambient daylight. Dark adaptation speedwas determined using a sensitive and reliable benchmark known as the rodintercept. The rod intercept is the time for scotopic sensitivity torecover to 5×10⁻⁴ cd/m².

Dark adaptation functions were measured using an AdaptDx darkadaptometer (Apeliotus Technologies, Inc.) as described in Example 1above as modified below. Dark adaptation curves were generated usingmethods known in the art. FIG. 7 compares two dark adaptation curvesfrom the same test subject. In the first case (FIG. 7A), photobleachingwas accomplished using a bright, achromatic white flash photobleachgenerated by a xenon arc light source producing a broad, relatively flatspectrum of light (5500 Kelvin color temperature) spanning the entirerange of cone and rod sensitivity and having an intensity of 6.38 logscot Td sec⁻¹, which is well above the intensity of ambient daylight. Inthe second case (FIG. 7B) photobleaching was accomplished using with adim (10 cd/m²) uniform bleaching field for 1-minute, which is well belowthe intensity of ambient daylight levels. The rod intercept in responseto the bright, achromatic white flash photobleach was 6.97 minutescompared with 2.54 minutes for the dim background photobleaching. Thecone-mediated portion of the dark adaptation function (the first fourthresholds in FIG. 7A) is effectively eliminated by using the dimphotobleaching procedure. Thus, use of a photobleaching light having anintensity less than the intensity of ambient daylight can dramaticallyshorten the duration of a dark adaptation test.

Example 5 Effect of Eccentricity on Dark Adaptation in Age-RelatedMaculopathy

In this example, a comparison was made between dark adaptation curvesgenerated by measuring dark adaptation at positions 5° and 12° on theinferior vertical meridian, using both normal test subjects and testsubjects with age-related maculopathy (ARM).

Dark adaptation functions were measured using an AdaptDx darkadaptometer (Apeliotus Technologies, Inc.) as described in Example 1above as modified below. Dark adaptation function was measured inresponse to a 4° diameter photobleaching light (provided as a flash)with an intensity of 6.38 log scot Td sec⁻¹. In this example, thephotobleaching light was the essentially white, 5500 Kelvin colortemperature broad spectrum light (having wavelengths from about 400 nmto about 700 nm) generated by the xenon arc source incorporated in thedark adaptometer. The target stimulus light was a 2° diameter, 500-nmcircular spot centered within the area subjected to photobleaching.Scotopic threshold measurements began immediately after photobleachoffset. During threshold measurement the subject focused on the fixationlight and responded when the stimulus was judged to be present bypushing a button. Threshold was estimated using a 3-down/1-up modifiedstaircase procedure. Approximately one threshold was measured eachminute for 20 minutes. Dark adaptation speed was determined using asensitive and reliable benchmark known as the rod intercept. The rodintercept is the time for scotopic sensitivity to recover to 5×10⁻⁴cd/m². The dark adaptation impairment of the ARM patients was calculatedrelative to a control group of age-matched adults.

Anatomical studies have shown that the area of greatest rod dysfunctionassociated with ARM is within the parafoveal region (3° to 5°eccentricity) of the retina. The pattern of scotopic sensitivityimpairment exhibited by ARM patients is consistent with the anatomicalfindings; that is, scotopic sensitivity impairment is greatest in theparafoveal region and decreases as a function of eccentricity towardsthe retinal periphery. In this example, we examined whether darkadaptation impairment has a similar pattern of dysfunction.

A total of 5 normal old adults and 8 ARM patients were tested. Groupassignment was based on grading of fundus photographs using the AREDSAMD Severity Classification System. Best-corrected visual acuity (ETDRSchart) and contrast sensitivity (Pelli-Robson chart) were measured onthe day of testing. Dark adaptation function was measured as describedabove. Each participant had their dark adaptation function measured onthe inferior vertical meridian at 5° and 12° on separate testing days.Both groups were similar in age, test eye acuity, and test eye contrastsensitivity. Dark adaptation impairment for the AMD group relative tothe normal old adults was almost 5 minutes greater at 5° than it was at12°. Furthermore, for the AMD group dark adaptation was almost 3 minutesslower at 5° than at 12° for the AMD group, whereas for the normal oldadults dark adaptation was almost 3 minutes faster at 5° than at 12°.

Patients in the ARM group exhibit greater dark adaptation impairment inthe parafoveal region compared to an area adjacent to the macula. Ingeneral, the AMD group's dark adaptation was slower in the parafovealregion compared with the more peripheral point; whereas, the normal oldadults exhibited the opposite pattern. These results show that tailoringthe region of the retina that is subject to photobleaching andsubsequent testing to the pattern of dysfunction for a particulardisease, for example, by choosing a region of the retina with maximumdisease susceptibility, or by comparison of one or more areas havingdifferent disease susceptibilities in a single test, may be useful inthe design of a diagnostic aimed at detecting the earliest stages of adisease. While this principle was illustrated in the current exampleusing ARM, it is equally applicable to other disease states.

Example 6 Effect of Photobleaching Light Spectrum on Detection ofAge-Related Maculopathvy

In this example, a comparison was made between dark adaptation curvesgenerated by measuring dark adaptation with achromatic and greenphotobleaching lights, using both normal test subjects and test subjectswith age-related maculopathy (ARM).

Dark adaptation functions were measured using an AdaptDx darkadaptometer (Apeliotus Technologies, Inc.) as described in Example 1above as modified below. In one case, an achromatic bleaching light(essentially white, 5500 Kelvin color temperature broad spectrumconsisting of wavelengths from about 400 nm to about 700 nm) wasgenerated by the xenon arc light source incorporated in the darkadaptometer, with the intensity of the flash set at 6.38 log scot Tdsec⁻¹(FIG. 8A). In the other case, a green bleaching light (about 490 nmto about 510 nm) was generated by placing a narrow green bandpassinterference filter (Edmund Optics NT43-169) over the face of the xenonarc flash incorporated in the dark adaptometer, with the intensity ofthe flash set at 7.03 log scot Td sec⁻¹(FIG. 8B). These two conditionsproduce nearly equivalent photobleaching of the photoreceptor visualpigments.

In both cases a normal adult and an ARM patient were tested. Theresponse patterns for the achromatic and green photobleaching lights arethe same, with the ARM patient exhibiting markedly slowed darkadaptation relative to the normal adult in both cases. Jackson andEdwards (A Short-Duration Dark Adaptation Protocol for Assessment ofAge-belated Maculopathy, Journal of Ocular Biology, Diseases, andInformatics; in press 2008, incorporated herein in its entirety byreference) have shown that measurement of dark adaptation using anachromatic photobleaching light is a sensitive and specific diagnosticfor ARM. The results of this example show that the ability todiscriminate ARM is preserved when using a green bleaching light,allowing the added benefit of lower patient burden and lower confoundfrom lens opacity without loss of diagnostic utility.

The foregoing description illustrates and describes the methods andother teachings of the present disclosure. Additionally, the disclosureshows and describes only certain embodiments of the methods and otherteachings disclosed, but, as mentioned above, it is to be understoodthat the teachings of the present disclosure are capable of use invarious other combinations, modifications, and environments and iscapable of changes or modifications within the scope of the teachings asexpressed herein, commensurate with the skill and/or knowledge of aperson having ordinary skill in the relevant art. The embodimentsdescribed hereinabove are further intended to explain best modes knownof practicing the methods and other teachings of the present disclosureand to enable others skilled in the art to utilize the teachings of thepresent disclosure in such, or other, embodiments and with the variousmodifications required by the particular applications or uses.Accordingly, the methods and other teachings of the present disclosureare not intended to limit the exact embodiments and examples disclosedherein. All references cited herein are incorporated by reference as iffully set forth in this disclosure.

What is claimed:
 1. A method for photobleaching a subject's eye, saidmethod comprising the steps of: a. exposing at least a portion of aretina of the subject's eye to a photobleaching light having at leastone of an intensity that is at or below the intensity of ambientdaylight and a tailored wavelength spectra within the visible spectrumto photobleach at least a portion of at least one visual pigment in theretina; b. using a psychophysical test to monitor a response, whereinthe exposure to the photobleaching light alters the response.
 2. Themethod of claim 1, wherein the photobleaching light accentuates orminimizes the response of a subset of photoreceptors to thephotobleaching light.
 3. The method of claim 1, wherein thepsychophysical test measures dark adaptation, photopic sensitivity,scotopic sensitivity, visual acuity, contrast sensitivity, colorsensitivity, color discrimination, visual field or a combination of theforegoing.
 4. The method of claim 1, wherein the psychophysical test iscolorimetry, dark adaptometry, a visual sensitivity test, a contrastsensitivity test, a spatial resolution acuity test, a photostress test,a flicker photometry test, a Vernier acuity test, a motion detectiontest, an object recognition test or a perimetry test.
 5. The method ofclaim 1, wherein the tailored wavelength spectra is selected topreferentially photobleach at least a portion of the visual pigment in arod photoreceptor, a short, wavelength cone photoreceptor, a mediumwavelength cone photoreceptor, a long wavelength cone photoreceptor, aretinal ganglion cell or a combination of the foregoing.
 6. The methodof claim 1, wherein the visual pigment is rhodopsin, the visual pigmentin the short wavelength cone photoreceptor, the visual pigment in themedium wavelength cone photoreceptor, the visual pigment in the longwavelength cone photoreceptor, melanopsin or a combination of theforegoing.
 7. The method of claim 1, wherein the tailored wavelengthspectra consists essentially of a wavelength selected from the groupconsisting of: a wavelength of about 505 nm, a range of wavelengthscentered on 505 nm, a wavelength of about 419 nm, a range of wavelengthscentered on 419 nm, a wavelength of about 531 nm, a range of wavelengthscentered on 531 nm, a wavelength of about 558 nm, a range of wavelengthscentered on 558 nm, a wavelength of about 460 nm, a range of wavelengthscentered on 460 nm, a wavelength of about 650 nm, a range of wavelengthscentered on 650 nm, a wavelength of about 410 nm, a range of wavelengthscentered on 410 nm, a wavelength of about 570 nm, or a range ofwavelengths centered on 570 nm, and a wavelength or range of wavelengthsover about 480 nm.
 8. The method of claim 1, wherein the tailoredwavelength spectra consists essentially of a range from about 490 nm toabout 510 nm or a range from about 600 nm to about 700 nm.
 9. The methodof claim 1, where the tailored wavelength spectra excludes wavelengthsof light in the blue spectrum and reduces measurement variabilityintroduced by lens opacity.
 10. The method of claim 1, wherein thetailored wavelength spectra maximizes absorption due to lens opacity orminimizes absorption due to lens opacity.
 11. The method of claim 1,wherein the psychophysical test further comprises exposing at least aportion of the retina to a target stimulus light.
 12. The method ofclaim 11, wherein the target stimulus light source has a tailoredwavelength spectra.
 13. The method of claim 12, wherein the tailoredwavelength spectra of the photobleaching light and the tailoredwavelength spectra of the target stimulus light are different from oneanother or are the same as one another.
 14. The method of claim 13,wherein the tailored wavelength spectra of the photobleaching light andthe tailored wavelength spectra of the target stimulus light consistessentially of about 500 nm or a range centered on 500 nm or consistessentially of about 650 nm or a range centered on 650 nm.
 15. Themethod of claim 1, wherein the photobleaching light has a set intensity.16. The method of claim 15, wherein the set intensity is at or below4.05 log scot Td/sec or at or below 3.15 log scot Td/sec.
 17. The methodof claim 1, wherein the portion of the retina exposed to thephotobleaching light is an area of the fovea, an area of the parafoveaor a combination of the foregoing.
 18. The method of claim 1, whereinthe portion of the retina exposed to the photobleaching light isentirely inside the fovea, is entirely inside the macula, is in theperipheral retina, is located on the inferior vertical meridian, islocated on the superior vertical meridian or is located at about 0° toabout 0.5° eccentricity, is located at about 2° to about 10°eccentricity, is located at 3° to 10° eccentricity, or is located atabout 10° to about 30° eccentricity.
 19. The method of claim 1, whereinthe portion of the retina exposed to the photobleaching light is anannular region, the annular region completely excluding the fovea, theannular region having an inner edge located at or outside about 2° andan outer edge located at or inside about 10° eccentricity.
 20. Themethod of claim 1, wherein the portion of the retina exposed to thephotobleaching light covers an area of about 4° of visual angle to about6° of visual angle.